1. Field of the Invention
This invention relates to novel azo compounds, metal complex compounds thereof, water-soluble azo dyes containing the azo compounds or metal complex compounds, and polarizing films having high durability and high polarity, said polarizing films being made of polymer films dyed with the dyes as dichroic dyestuff and oriented.
2. Description of the Related Art
It is now the common practice to produce a polarizing film by dyeing a stretched and oriented film of polyvinyl alcohol or a derivative thereof or an oriented film of a polyene with iodine or a dichroic dye as a polarizing element.
Among such polarizing films, those making use of iodine as a polarizing element are excellent in initial polarizing ability but are weak against water or heat. They are hence accompanied by a problem in durability when employed over a long period of time under high temperature and humidity conditions. To improve their durability, it has been proposed, for example, to intensify their treatment in an aqueous solution containing formaldehyde or boric acid or to use, as a protective film, a polymer film having low moisture permeability. Their durability is however still insufficient under high temperature and moisture conditions.
Polarizing films making use of a dichroic dye as a polarizing element, compared with polarizing films using iodine, have better resistance against water and heat but are inferior in polarizing ability. With a view toward improving this drawback, polarizing films using an organic dye as a polarizing element and having improved hydrothermoresistance and polarizing ability are proposed in Japanese Patent Laid-Open Nos. 145255/1984, 156759/1985 and 168743/1985; and U.S. Pat. Nos. 4,514,559 and 4,859,039.
When employed as polarizing films, such organic dyes are generally used in combination with a dye having absorption in a particular wavelength range to provide the polarizing films with a neutral color. It is therefore the current situation that depending on the dyes employed, such polarizing films may undergo (1) a substantial color change at high temperatures, (2) a substantial change in polarizing ability due to the type of the dye employed for obtaining the neutral color or (3) color irregularity depending on the dyeability of the dyes.